


Dirty Secrets

by LittleSinners



Category: Undertale (Video Game)
Genre: Alternate Universe - Underswap, Begging, Dom/sub, Ecto-Penis (Undertale), Ecto-Tongue (Undertale), F/M, Female Reader, I'm a filthy sinner, Master/Slave, Orgasm Denial, Plot What Plot/Porn Without Plot, Skeleton Sex (Undertale), Smut, reader has vagina, shameless porn
Language: English
Status: Completed
Published: 2016-07-29
Updated: 2016-07-29
Packaged: 2018-07-27 13:30:02
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,375
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7619944
Author URL: https://archiveofourown.org/users/LittleSinners/pseuds/LittleSinners
Summary: <blockquote class="userstuff">
              <p>Sans is looking for a birthday present idea to give to the human and searches her room for one. What he finds is something very different.</p>
            </blockquote>





	Dirty Secrets

US!Sans X Dom!Reader : Dirty secret

Sans couldn't stop pacing around the room and looking at the callendar. Your birthday was tomorrow and he still couldn't figure out what to get for you! He wanted it to be a surprise so he couldn't ask you what you would've liked, and he just couldn't find any idea about what to give you. He wanted to make you happy! You'd been staying with him and Papyrus for about a year now, he needed to make your first birthday in the underground feel special! But he just had no idea what to give you..

'W-What am I going to do! The magnificent Sans must have the most magnificent present for the human!'

An idea had sprouted into his mind a few days ago but he'd always pushed it away.

'I could look through her room.. Her birthday is tomorrow after all.. Ugh, but I don't want to invade her privacy! Thats rude! The magnificent Sans is anything but rude!'

He hung his head in defeat.

'But I don't have much of a choice.. There's very little time left.. I HAVE TO! FOR THE HUMANS BIRTHDAY!'

Knowing you weren't home, he rushed excited to your room, and closed the door behind him.

'Mweheheh.. Now where to start looking..'

The room itself was neatly cleaned, a wardrobe, a nice clean bed, and a bedside table, there had to be clues somewhere in there! First step, the bed! He looked everywhere under it, but nothing to be found except dust.

'Oh.. Nothing. But that will not discourage the magnificent Sans!!'

He rushed over to the wardrobe and threw it open, looking through the clothes and trying to find if something was hiden. Only to stumble upon, skirts, pants, shirts, shorts and..  
'P-Panties? O-OH GOD WHAT ARE THOSE THEY JUST LOOK LIKE A FEW STRINGS! I-I never knew the human had such lewd things! W-Why?' He couldn't take his eyes off of them for about 5 minutes, shamefully imagining the curves of your hips only covered by those few strings and the small piece of cloth hiding your privates, until the embarassment was too much for him and he finally put them back. Ignoring or maybe even not noticing the blue, glowing erection in his pants.

'Thats enough now.. Keep your mind on the task Sans, finding a magnificent gift for the human!!'

His last chance was the drawers of your bedside table. The bottom drawer was empty save for two books, a heart shaped locket and a torn ribbon. However, the top drawer, to his surprise was locked.

'This has to be it! I have to use my magic to unlock it! Maybe she has a diary or something and I could find out what I need! But even then I'm just so curious about it.. Why would she be hiding something from us?'

His magic surrounded the lock, twisting and clicking at the mechanism. Until finally the lock turned. He jumped and made a little squeal of victory before pulling the handle and openning the drawer.

'Alright.. Lets see what we- Uh?.. A- A collar? Me and Pappy don't have a pet besides his pet rock why would she need that.. And what are those beads? This isn't long enough to be a necklace.. And this flat wooden thingy.. A-And this.. O-OH STARS. IS THAT A.. P-P.. OH STARS WHY DOES SHE HAVE THIS! I-ITS SO BIG TOO, DOES SHE REALLY.. D-DO THAT? Wait whats that switch at the b-bottom.. O-OH NO WHY DOES IT VIBRATE THIS IS SO WEIRD! WHY WOULD THE HUMAN HAVE SUCH A-'

He was cut off by a faint 'click'. What sounded like the door.. Locking.

'Oh no..' he thought to himself, frozen in place.

"Well well.. Look what we have here.." A grin spread across your face. "What a sneaky boy you are.. Going into my room, openning my drawers. Looking through my things. Finding my.. Toys."

"H-HUMAN!! I- I.. IMSORRYIWANTEDTOFINDYOUABIRTHDAYPRESENTANDIENDEDUPLOOKINGTHROUGHYOURSTUFFANDIFOUNDTHISDON'THURTMEPLEASE!!" He said loudly, a blush covering nearly his entire skull as he put down your vibrator back into its drawer.

"Oh my sweet little blueberry, what makes you think I would hurt you.. But what I will do however is punish the bad little boy that you are."

"I-I WON'T TELL A SOUL I PROMISE!"

"I know, but just as a precaution. I'll make sure to fuck you so hard the only thing you'll be able to say is my name."

He wimpered and backed up a bit when you got closer. Before pushing him down onto the bed and swiftly locking the collar around his cute little neck.  
"Now.. Be a good boy. And call me mistress."

He seemed so embarassed. Even a bit scared, but he seemed to slowly be getting into it. The way you were ontop of him, looking down at him like that holding his leash into your fist and pulling it. It made him feel so strange. These urges he'd never felt them. But now he was, and they were so, so strong. It made each of his bones feel like they were on fire. 

He was losing it, but it felt so.. so good.

"M-Mistress.."

"Good boy.. Now lets get on with your punishment."

Quickly, you pushed his shirt over his head, and pulled his pants down. He was already at your mercy and didn't make much of a move to stop you. Now.. for the fun part.

You began by trailing long licks on his collarbone. You knew it was his first time, and knowing how sensitive he was too made your hunger even stronger.

You dragged your nails, teeth and tongue against every nook and cranny of his bones you could find until he was a wimpering, crying and twitching mess underneath you, begging for more. You finally pulled down the last article of clothing retaining him. His twitching and throbbing cock was already dripping for your attention. And he was moaning and begging for you to touch him more.

"How cute.. Fine, I will attend to you. First let me get something."

Your hands fumbled a bit inside of the drawer until you pulled out something that looked like "A- A ring? Human why do you- A-AHH!!" It took you very little time to adjust the cock ring to his lenght so he wouldn't cum, this was a punishment after all.

And immediately, you got to sucking. Your soft slips encasing his cock felt like heaven, and your warm and wet tongue licking at the glass-like texture of his cock left him almost screaming. His cyan blue tongue lolled out lewdly, his saliva dripping down his chin and tears brimming his eyes.

"M-MISTRESS PLEASE!! MORE I'M.. I'M GOING TO.. A-AA- W-WHY CAN'T I..? MISTRESS WH-AAT DID YOU DOOO?"

It was so much for him, too much, he started crying, sobbing, ripping at the bedsheets with bony fingers, it was so much, too much.

Taking his twitching, swollen lenght out of your mouth with a 'pop', you got ready for the main course. Taking off your clothes and your underwear first, you positionned yourself above him.

"N-NO NO PLEASE! I CAN'T HANDLE TH-IIIIIIISSS!! AAA- AAAHHH!! MISTRESS PLEASE ITS TOO MUCH! ITS TOO GOOD!!" The slow pace you had taken got faster and faster. "I'M GONNA DIE!! PLEASE I'M GONNA DIE!! ITS TOO H-HOT!" His mouth hung open lewdly, his breathing was shallow and raspy from how much he'd screamed. You would alternate between moving his lenght in and out of you as fast as possible, and sometimes taking him to the hilt before gyrating your hips to let him feel the inside of you even more. Throughout the ride, you'd came about two times. But really, half the fun in this was just watching him. You lifted yourself off of him, a brief look of confusion crossing his eyes before you slowly took off the ring. A long, high-pitched, dragged-out moan of relief leaving him when about a glassfull of cum came out of him, dripping all over your face, which you licked off hungrily.  
The sun had already settled down, and before he fell into a sweet, blissfull sleep. His last words for the night were.

"Happy birthday ______.. I love you."

**Author's Note:**

> There you have it. My first upload to this website. Hope you enjoy it!


End file.
